This invention relates to an apparatus for measuring the sliver thickness in a drawing frame, particularly in a regulated drawing frame. The apparatus includes a sliver guiding device for guiding a plurality of simultaneously inputted fiber slivers at the inlet of the drawing frame. At least parts of the inner wall faces of the guiding device converge such that the side-by-side running slivers are brought together to form a sliver assembly in which the slivers assume a side-by-side contacting relationship in a single plane. Downstream of the guiding device, as viewed in the direction of sliver run, a roller pair is arranged which defines a nip through which the sliver assembly passes. By virtue of the frictional engagement in the nip, the roller pair pulls the sliver assembly through the sliver guiding device. Downstream of the roller pair the slivers diverge from one another. The sliver guiding device is associated with a biased, movable sensor element which, together with an operationally stationary counterelement (wall element), constitutes a constriction for the throughgoing sliver assembly. The sensor element executes excursions as the thickness of the sliver assembly changes. The displacements of the sensor element are applied to a transducer which, in response, generates control pulses. The counterelement situated opposite the sensor element may be adjusted and immobilized in its adjusted position.
In a known apparatus of the above-outlined type two sliver guiding devices are connected in series. The simultaneously running slivers first enter the upstream-located, first sliver guiding device and are pre-densified thereby. The first sliver guiding device is at a small clearance from the downstream-located, second sliver guiding device, so that air may escape through the clearance. The clearance thus functions as an air vent. The first sliver guiding device--similarly to the second sliver guiding device--has two converging lateral surfaces, as well as top and bottom surfaces and--with the exception of inlet and outlet openings--is thus closed on all sides. In the first sliver guiding device the slivers are preformed into a sliver assembly which is pre-densified, while air is pressed out therefrom. By virtue of the fact that the top and bottom surfaces too, converge in the advancing direction of the sliver, the sliver assembly may not deflect upwardly or downwardly, but is forced through the outlet opening of the first sliver guiding device and compressed. The withdrawing roll pair has to pull the slivers through both sliver guiding devices.